Today, the number of disks (magnetic disks) included in a magnetic disk device is increasing. In accordance with the increase in the number of disks, the number of heads (magnetic heads) is also increasing. The magnetic disk devices have a signal processing circuit including a read amplifier circuit for processing (for example, amplifying) a signal read by a selected head, and sending the processed signal to a transmission path. The signal processing circuit includes a write driver circuit for converting, into a write current, a write signal transferred through another transmission path, and sending the write current to a selected head. In general, the signal processing circuit is formed in an integrated circuit (IC) of a single package. The IC is generally referred to as a preamplifier IC (or a head IC).
Conventionally, a single preamplifier IC is used to operate a plurality of heads included in a magnetic disk device. The preamplifier IC is generally mounted on a flexible printed circuit (FPC) board.
On the other hand, a magnetic disk device of one type includes, on a FPC board, a plurality of preamplifier ICs of the same configuration corresponding to a plurality of heads, respectively. In general, the FPC board is connected through a connector to a large-scale integrated circuit (LSI), called a system-on-a-chip (SOC), wherein a plurality of circuits are integrated on a single chip. More specifically, a plurality of preamplifier ICs on the FPC board are connected to a main LSI through a transmission path.
The transmission path is used for transmitting a signal at a high speed between the main LSI and (one of) the plurality of preamplifier ICs. During the high-speed transmission, in order to prevent signal disorder, it is preferable to make the impedance of the main LSI match the impedance of the transmission path and the impedance of the transmission path match the impedance of the preamplifier ICs.